1. Field of the Invention
The present invention relates to a cassette holder, and more particularly, to a cassette holder for cleaning equipment.
2. Description of the Prior Art
In current semiconductor processes, automatic cleaning equipment is some of the most fundamental and common fabrication equipment. The automatic cleaning equipment uses a robot to move a cassette carrying semiconductor wafers between acid tanks and water tanks, automating surface cleaning of the semiconductor wafers. To prevent the robot from losing the cassette, a loading plate is usually placed at the bottom of the acid or water tank. The loading plate prevents the cassette from moving, and thus prevents it from being misplaced and hence irretrievable to the robotic arm.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of automatic semiconductor cleaning equipment 10 according to the prior art. The cleaning equipment 10 comprises a robot (not shown), a solution tank 12, a plurality of pipes 14 positioned on an internal wall of the solution tank 12, a cassette 16 in which a plurality of semiconductor wafers are placed, and a cassette holder 20 in the solution tank 12. The cassette holder 20 can hold two cassettes 16. The pipes 14 usually comprise a thermal couple thermometer 22, a barometric level sensor 24, a heater 26, a supply pipe 28 and an aspirator 30. The cleaning equipment 10 is usually equipped with three or four heaters 26, though FIG. 1 shows only one heater 26.
The cassette holder 20 comprises a loading plate 32, a plurality of guide blocks 34 mounted on the loading plate 32, and a plurality of feet 36 supporting the loading plate 32. The cassette holder 20 uses guide blocks 34, two in each direction, to prevent any displacement of the cassette 16.
In semiconductor processes, a hot-acid solution is usually used as an etching or cleaning solution. The solution tank 12, therefore, is made of quartz, which is resistant to both heat and acid. Similarly, the loading plate 32 is formed by welding quartz rods together (usually called a quartz frame). Such a frame is resistant to the hot-acid solution. The cassette holder 20 is quite light, and may be uplifted by the underlying heater 26, or by buoyancy. In overcome buoyancy of the cassette holder 20, the loading plate 32 is often made of large-diameter quartz rods to increase its weight and improve its structural integrity. However, in the event of errors or accidents the thicker quartz rods may cause the solution tank 12 crack. For example, the robot may fail to remove the cassette 16 from the solution tank 12, and another cassette is then put into the solution tank 12 on top of the cassette 16. Overloading of cassettes can cause serious damage to the cassette holder 20, such as breaking the loading plate 32.
Furthermore, although a Teflon holding plate 38 is employed to fix each of the pipes 14 to the top of the wall of the solution tank 12, the bottoms of the pipes 14 that extend into the solution tank 12 are not sufficiently restricted. After the pipes 14 have been exposed to the hot-acid solution for a period of time, the bottoms of the pipes 14 may distort and push against the cassette 16, leading to misplacement of the cassette 16. This, in turn, can lead to accidents during the automatic transfer process.
In order to prevent the acid solution from evaporating, a hood (not shown) covers the solution tank 12. This hinders the operator from observing the solution level in the solution tank 12. The operator can check the solution level only when the hood is opened, but the operator must check the level quickly as the hood closes in a short while after the cassette 16 is placed into the solution tank 12. The solution tank 12 does employ the barometric level sensor 24 to check the level of the acid solution in the solution tank 12. The barometric level sensor 24 is full of nitrogen gas. Different solution levels cause different gas pressures within the barometric level sensor 24. A level panel (not shown) uses a set of six variable resistors to generate the level signal.
In practice, however, there is no steady reference point for the solution level. Most operators adjust the solution level based upon experience. Thus, the solution level isn""t controlled precisely and scientifically. If the solution level is too high, the acid solution is wasted and may flow over the solution tank 12. If solution level is too low, the upper portion of the wafer 18 may lack sufficient chemical treatment, causing defects to the wafer 18.
It is therefore a primary objective of the present invention to provide a cassette holder for cleaning equipment to solve the above-mentioned problem.
In a preferred embodiment, the present invention provides a cassette holder positioned in cleaning equipment. The cleaning equipment comprises a solution tank, at least one pipe positioned on an internal wall of the solution tank, and at least one cassette in which at least one semiconductor wafer is placed. The cassette holder has a loading plate in the solution tank for holding the cassette. There are pluralities of guide blocks mounted on the loading plate to prevent movement of the cassette, and a side-frame positioned at an end of the loading plate proximate to the pipe. The side-frame is designed for disassembly and serves as a shield between the pipe and the cassette that prevents the pipe from pushing against the cassette. The side-frame comprises a horizontal rod that serves as a level index for the solution tank. The bottom of the loading plate has a plurality of neck feet, and once a neck foot suffers a force that exceeds a normal value, the neck foot will break. A Teflon tube that enhances the support strength of the neck foot covers each neck foot. The cassette holder further comprises at least one weight to overcome buoyancy of the cassette holder.
It is an advantage of the present invention that the cassette holder has the side-frame that prevents the pipe from pushing against the cassette. The side-frame includes the horizontal rod that serves as a level index for the solution. The bottom of the loading plate has a plurality of neck feet, which prevents the loading plate from impacting the solution tank during accidents in the transfer process. The cassette holder uses the weight to overcome buoyancy of the cassette holder.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.